Generally described, a metal-air cell, such as a zinc-air cell, uses one or more air permeable cathodes separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the one or more cathodes to produce hydroxide ions. The metallic zinc anode is then oxidized by the hydroxide ions. Water and electrons are released in this electrochemical reaction to provide electrical power.
Initially, metal-air cells found limited commercial use in devices, such as hearing aids, which required a low level of power. In these cells, the air openings which admitted air to the air cathode were so small that the cells could operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the water vapor pressure within the cell. However, the power output of such cells was too low to operate devices such as camcorders, cellular phones, or laptop computers. Furthermore, enlarging the air openings of a typical "button cell" was not practical because it would lead to premature failure as a result of flooding or drying out
In order to increase the power output of metal-air cells so that they could be used to operate devices such as camcorders, cellular phones, or laptop computers, air managers were developed with a view to providing a flow of reactive air to the air cathodes of one or more metal-air cells while isolating the cells from environmental air and humidity when no output is required. As compared to conventional electrochemical power sources, metal-air cells containing air managers provide relatively high power output and long lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as the reactant in the electrochemical process as opposed to a heavier material such as a metal or a metallic composition. Examples of air managers are shown in U.S. Pat. Nos. 4,913,983, 5,356,729, and 5,691,074.
Attempts have been made to design a metal-air cell to fit the form of a standard "D" or "AA" cylindrical alkaline cell. Cylindrical batteries without air managers are shown in U.S. Pat. No. 3,697,326 and European Published Application No. 1,459,135. The lack of success of these designs likely is attributable to an inability to provide high enough power output for devices typically operated by conventional standard sized cylindrical cells without providing large air openings that allow the cells to flood or dry out.
Thus, there is a need in the art for a standard size cylindrical metal-air cell that can provide a power output level sufficient to operate electrical devices, whether individually or in groups inserted into a battery compartment of such devices. Such a cell also should not flood or dry out when inserted into such devices and left unattended during extended periods of non-use.